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atmospheric stability

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Atmospheric stability is very important to the change of climate because it controls precipitation. When air is stable, precipitation would not occur. When air is unstable, condensation and precipitation would occur. When air is conditionally stable, condensation and precipitation may or may not occur. To understand atmospheric stability, we must first understand the importance of lapse rate. There are three types of lapse rate, they are the environmental lapse rate, the dry adiabatic lapse rate and the wet adiabatic lapse rate. Temperature drops with altitude at an average rate of 6.4C/1000m. This average value is known as the environmental temperature lapse rate. This is the observed temperature distribution with height under stable cloudless atmospheric conditions at a given time and place. ...read more.


This is known as the dry adiabatic lapse rate. One difference between the dry and saturated adiabatic lapse rates is that whereas the former remains constant the later varies with temperature. This is because saturated adiabatic lapse rate depends upon the amount of heat released by condensation which in turn depends upon the moisture content and therefore the air temperature. Contrast between the environmental lapse rate and the adiabatic lapse rates controls the stability of the atmosphere. There are three types of stability. The first one is absolute stability. Stable atmospheric conditions prevail when the environmental lapse rate is less than the saturated adiabatic rate. An example of this condition is shown in figure 1. ...read more.


In other words, the parcel is colder and denser than the surrounding air at 1000 meters. If the uplift mechanism ceased, the parcel of air would return to the surface. Air is unstable when the environmental lapse rate is greater than the dry adiabatic rate. Under these conditions, a rising parcel of air is warmer and less dense than the air surrounding it at any given elevation. Figure 2 depicts unstable conditions. Follow up the graph for the rising parcel of air. Note that at any elevation above the surface the parcel temperature is higher than the air that surrounds it. Even as it reaches the dew point temperature at 2000 meters, the air remains warmer than the surrounding air. As a result, it continues to rise and cool at the saturated adiabatic rate. Vertically developed cloudes are likely to develop under unstable conditions such as this. ...read more.

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